[python-experimental] improves type hints of optional object properties

Created by: spacether

for optional object properties, adds schemas.Unset type hints

Note: If one wanted to make the get_item type hints work better, one could define an enum for the field names Then the field names would be

• name: FieldName(Enum) when they exist in properties
• name: str for additionalProperties

And with that, the overloading will work correctly. Right now it is not working right for some_dict["someProp"] because when someProp exists and is a string literal, that literal is also type string, so it also matches with the str (additionalProperties) type hint.

Question: do pycharm and vscode see field_name = FieldName("someField") as the correct enum value type? If not then one may be able to add a type hint showing that.

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